ALLERGIES: INTERVIEW WITH THE EXPERT
Sneezing, eye tearing, coughing, itching, breathing difficulties: every year the spring season inaugurates a series of annoying symptoms that, unfortunately, allergy sufferers know very well. It is estimated that allergic rhinitis only affects on average 24% of the European population.
What does it mean to be allergic? Why are some allergies more common than others? What therapies are currently available? What research is the San Raffaele conducting in this regard? We talked about this with Dr. Samuele Burastero, an allergist physician, Group Leader of the Cellular and Molecular Allergology Unit at the San Raffaele Hospital who, in this interview, makes things clearer.
Dr. Burastero, why are we allergic?
Allergy is an abnormal immune reaction against totally harmless foreign substances. The immune system of the allergic person “makes a mistake” by identifying a harmless substance, called allergen, as a dangerous microorganism. The immune recognition mechanism is the same that activates against bacteria, viruses or parasites. It is therefore an immune dysfunction, as in the case of autoimmune diseases, but much more frequent and, on average, much less serious.
In any case it is wrong to consider the allergy as a “weakness” of the immune system, since it represents the result of an error due to excess – and not to a lack – of response.
Why are some allergies (pollen, animal fur...) more frequent than others?
The term “antigens” refers to the components of viruses, bacteria or parasites correctly recognized by the immune system of mammals, in order to defend the organism from the respective aggressions. In people with allergies, also perfectly harmless substances, the allergens, act as antigens. The characteristics that make an antigen an allergen have been actively investigated in the last two decades, yet they are not completely known.
Presently, there is general consensus that in most cases allergens, which are glycoproteins [proteins conjugated to carbohydrates, i.e. sugars, Editor’s Note], have molecular characteristics resembling those of the most important proteins in the immune response against parasites. This is consistent with the fact that domestic mites are the most frequent cause of respiratory allergy, and at the same time they belong to the same family as some parasites. In the case of pollens or pet allergens, the apparently random similarity between the molecular structure of the main allergenic proteins and the proteins of some parasites has been observed.
Why can allergies also occur in adulthood or change over the years?
In addition to the intrinsic characteristics of the allergens, the development of an allergy is favored by the actual exposure to the allergen, in adequate doses, continuously and for a given route of exposure. For example, a cat allergy cannot develop in the absolute absence of contact with these animals. A second factor is genetic predisposition to the development of allergies and a third one the absence of factors hindering allergy onset, such as exposure to powders of farm animals containing bacterial components that protect against the development of allergies. When this complex set of factors occurs, allergy can ensue. However, over time allergen persistence tend to induce (physiologically) a certain degree of tolerance to allergen themselves, which may explain the fluctuation of clinical conditions.
May the organism get used to a certain allergen?
It is normal for the organism to “get used” to a certain allergen, even if this may take years or decades, depending on the subject, on the type of exposure and the amount and frequency of introduction of the allergen (by food or by inhalation, for instance). This process can be associated with allergen reactions of variable severity. The mechanism that presides over this phenomenon is immunological tolerance. Tolerance to allergens can be induced in a controlled and safe manner, rather than by natural exposure, by the continuous administration of standardized extracts containing the allergens involved in triggering the symptoms.
How can allergy be treated? What are the strengths and weaknesses of the treatments available so far?
Allergy is treated with two main drugs categories, those that treat symptoms (symptomatic) and those that treat the cause.
Drugs that treat symptoms are indicated in most case and they are aimed at countering the disorders in the organs in which they occur, for example the nose in the case of rhinitis, the eye in the case of conjunctivitis, the airways in the case of asthma. For this reason we use nasal sprays containing steroids (cortisone), eye drops containing antihistamines or cortisones, sprays or inhalation powders containing drugs that increase the diameter of the bronchi (beta-agonist bronchodilators, part of the adrenaline family, but with local action). In asthma, inhalation products containing cortisones are also used, mostly in association with bronchodilators.
The most used drugs in allergic rhinitis and conjunctivitis are antihistamines, which are taken orally and display an overall effect at both the nose and the eyes. Antihistamines have a good safety profile, but may cause drowsiness. There is not a single drug that can be considered the best available antihistamine, instead individual variability of the response applies to so-called second and third generation “non-sedating” antihistamines.
The treatment to the allergy causes is solely based on the administration of purified and standardized allergen extracts, sublingually or subcutaneously, in order to induce immunological tolerance (allergen-specific immunotherapy). Once the effect is established, this will last after suspension for a few years. However, to achieve this, immunotherapy should be continued for at least 3 years, which makes patients’ compliance with this treatment particularly low.
What researches is the San Raffaele conducting? On what do our studies focus the most, and what are/have been our main discoveries?
The San Raffaele has a clinical center of allergy and a research laboratory. The clinical center is part of the national network for severe asthma (Severe Asthma Network Italy, SANI), it has participated and still participates in clinical trials with drugs for immunotherapy and with monoclonal antibodies to combat allergic inflammation. One of the two drugs for the treatment of grass allergy registered in Italy has been approved with the contribution of our center. The laboratory, historically focused on the study of local immunity in the asthmatic lung, has been involved in recent years in the characterization of molecular allergens used in allergy diagnosis. The research allergy lab has developed over the years second level diagnostic tests that are currently available to all patients thanks to their implementation in San Raffaele clinical laboratory (ISAC microrarray, basophil degranulation test, diamino-oxidase determination).